1. Field of the Invention
This invention relates to respiration monitoring. More particularly, it relates to respiration monitoring using impedance measuring devices connected to electrodes attached to a human body.
2. Description of the Related Art
Current respiration monitoring utilizes a technique known as impedance respiration monitoring. This technique measures the impedance between two electrodes (typically right arm and left arm) to monitor airflow. As a subject inhales, air, which is an insulator, enters the lungs and causes the net impedance in the circuit to increase. When the subject exhales, air leaves the lungs and causes the impedance in the circuit to decrease.
The current lead measurement options, i.e., leads I and II, focus on measuring thoracic breathing, which is considered a standard method of breathing in most adults. Thoracic breathing involves using the intercostals to elevate the lungs to begin inspiration. Although the chest moves significantly, only a small amount of air is actually passed into the lungs and usually only as far as the middle lobes.
Given the current leads I and II placement, which defines a conductive path across the upper portion of the thorax, left arm (LA) and right arm (RA) electrodes are well suited to measuring thoracic breathing. However, there is another more efficient type of breathing known as “abdominal breathing,” which the traditional electrode placement is less effective at monitoring.
While thoracic breathing is normal in most conscious adults, children and adult subjects who relax, sleep or are otherwise unconscious, commonly adopt abdominal breathing.
Abdominal breathing occurs when the diaphragm becomes the controlling factor in the respiratory cycle. When the diaphragm controls breathing, each breath becomes deeper as more air enters the lower lobes of the lung where there is a higher concentration of blood vessels, allowing for more efficient gas exchange.
Abdominal breathing is the mode of respiration that humans use at birth because it is the most efficient. As humans grow, the conscious breathing pattern elevates to the chest to the point where we tend to forget abdominal breathing. Abdominal breathing is typical in unconscious adults. When an adult relaxes or falls asleep they will unconsciously revert back to the more efficient abdominal breathing.
As the subject transitions to abdominal breathing, the respiration signal provided by the arm electrodes is attenuated, since thoracic expansion is progressively reduced, even though the respiration is becoming more efficient. The attenuated signal could mistakenly suggest to an observer that respiration is getting worse, not better.
Thus, electrodes used to monitor respiration in their traditional ECG positions (i.e. the LA and RA electrodes) provide a respiration signal that is subject to motion artifact and is attenuated whenever the subject falls asleep. Further, the traditional placement does not indicate abdominal breathing, the dominant mode of respiration for children and unconscious adults.
What is needed therefore is a method of monitoring subject respiration that minimizes both motion artifact and cardiogenic artifact. What is also needed is a respiration monitoring method that produces a stronger signal. What is also needed is a method of monitoring respiration that would give the clinician a better option for monitoring abdominal respiration. What is also needed is a new respiration monitoring vector that will provide significant noise reduction and improved signal quality as compared to the traditional respiration monitoring vectors, i.e., leads I and II. These improvements would give clinicians more flexibility in respiration monitoring.